[ Upstream commit 6043b794c7668c19dabc4a93c75b924a19474d59 ]
During ILA address translations, the L4 checksums can be handled in different ways. One of them, adj-transport, consist in parsing the transport layer and updating any found checksum. This logic relies on inet_proto_csum_replace_by_diff and produces an incorrect skb->csum when in state CHECKSUM_COMPLETE.
This bug can be reproduced with a simple ILA to SIR mapping, assuming packets are received with CHECKSUM_COMPLETE:
$ ip a show dev eth0 14: eth0@if15: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000 link/ether 62:ae:35:9e:0f:8d brd ff:ff:ff:ff:ff:ff link-netnsid 0 inet6 3333:0:0:1::c078/64 scope global valid_lft forever preferred_lft forever inet6 fd00:10:244:1::c078/128 scope global nodad valid_lft forever preferred_lft forever inet6 fe80::60ae:35ff:fe9e:f8d/64 scope link proto kernel_ll valid_lft forever preferred_lft forever $ ip ila add loc_match fd00:10:244:1 loc 3333:0:0:1 \ csum-mode adj-transport ident-type luid dev eth0
Then I hit [fd00:10:244:1::c078]:8000 with a server listening only on [3333:0:0:1::c078]:8000. With the bug, the SYN packet is dropped with SKB_DROP_REASON_TCP_CSUM after inet_proto_csum_replace_by_diff changed skb->csum. The translation and drop are visible on pwru [1] traces:
IFACE TUPLE FUNC eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) ipv6_rcv eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) ip6_rcv_core eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) nf_hook_slow eth0:9 [fd00:10:244:3::3d8]:51420->[fd00:10:244:1::c078]:8000(tcp) inet_proto_csum_replace_by_diff eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) tcp_v6_early_demux eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_route_input eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_input eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_input_finish eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ip6_protocol_deliver_rcu eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) raw6_local_deliver eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) ipv6_raw_deliver eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) tcp_v6_rcv eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) __skb_checksum_complete eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) kfree_skb_reason(SKB_DROP_REASON_TCP_CSUM) eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) skb_release_head_state eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) skb_release_data eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) skb_free_head eth0:9 [fd00:10:244:3::3d8]:51420->[3333:0:0:1::c078]:8000(tcp) kfree_skbmem
This is happening because inet_proto_csum_replace_by_diff is updating skb->csum when it shouldn't. The L4 checksum is updated such that it "cancels" the IPv6 address change in terms of checksum computation, so the impact on skb->csum is null.
Note this would be different for an IPv4 packet since three fields would be updated: the IPv4 address, the IP checksum, and the L4 checksum. Two would cancel each other and skb->csum would still need to be updated to take the L4 checksum change into account.
This patch fixes it by passing an ipv6 flag to inet_proto_csum_replace_by_diff, to skip the skb->csum update if we're in the IPv6 case. Note the behavior of the only other user of inet_proto_csum_replace_by_diff, the BPF subsystem, is left as is in this patch and fixed in the subsequent patch.
With the fix, using the reproduction from above, I can confirm skb->csum is not touched by inet_proto_csum_replace_by_diff and the TCP SYN proceeds to the application after the ILA translation.
Link: https://github.com/cilium/pwru [1] Fixes: 65d7ab8de582 ("net: Identifier Locator Addressing module") Signed-off-by: Paul Chaignon paul.chaignon@gmail.com Acked-by: Daniel Borkmann daniel@iogearbox.net Link: https://patch.msgid.link/b5539869e3550d46068504feb02d37653d939c0b.1748509484... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Paul Chaignon paul.chaignon@gmail.com --- include/net/checksum.h | 2 +- net/core/filter.c | 2 +- net/core/utils.c | 4 ++-- net/ipv6/ila/ila_common.c | 6 +++--- 4 files changed, 7 insertions(+), 7 deletions(-)
diff --git a/include/net/checksum.h b/include/net/checksum.h index 1338cb92c8e7..28b101f26636 100644 --- a/include/net/checksum.h +++ b/include/net/checksum.h @@ -158,7 +158,7 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb, const __be32 *from, const __be32 *to, bool pseudohdr); void inet_proto_csum_replace_by_diff(__sum16 *sum, struct sk_buff *skb, - __wsum diff, bool pseudohdr); + __wsum diff, bool pseudohdr, bool ipv6);
static __always_inline void inet_proto_csum_replace2(__sum16 *sum, struct sk_buff *skb, diff --git a/net/core/filter.c b/net/core/filter.c index 99b23fd2f509..e0d978c1a4cd 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -1999,7 +1999,7 @@ BPF_CALL_5(bpf_l4_csum_replace, struct sk_buff *, skb, u32, offset, if (unlikely(from != 0)) return -EINVAL;
- inet_proto_csum_replace_by_diff(ptr, skb, to, is_pseudo); + inet_proto_csum_replace_by_diff(ptr, skb, to, is_pseudo, false); break; case 2: inet_proto_csum_replace2(ptr, skb, from, to, is_pseudo); diff --git a/net/core/utils.c b/net/core/utils.c index 27f4cffaae05..b8c21a859e27 100644 --- a/net/core/utils.c +++ b/net/core/utils.c @@ -473,11 +473,11 @@ void inet_proto_csum_replace16(__sum16 *sum, struct sk_buff *skb, EXPORT_SYMBOL(inet_proto_csum_replace16);
void inet_proto_csum_replace_by_diff(__sum16 *sum, struct sk_buff *skb, - __wsum diff, bool pseudohdr) + __wsum diff, bool pseudohdr, bool ipv6) { if (skb->ip_summed != CHECKSUM_PARTIAL) { csum_replace_by_diff(sum, diff); - if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr) + if (skb->ip_summed == CHECKSUM_COMPLETE && pseudohdr && !ipv6) skb->csum = ~csum_sub(diff, skb->csum); } else if (pseudohdr) { *sum = ~csum_fold(csum_add(diff, csum_unfold(*sum))); diff --git a/net/ipv6/ila/ila_common.c b/net/ipv6/ila/ila_common.c index 95e9146918cc..b8d43ed4689d 100644 --- a/net/ipv6/ila/ila_common.c +++ b/net/ipv6/ila/ila_common.c @@ -86,7 +86,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb,
diff = get_csum_diff(ip6h, p); inet_proto_csum_replace_by_diff(&th->check, skb, - diff, true); + diff, true, true); } break; case NEXTHDR_UDP: @@ -97,7 +97,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb, if (uh->check || skb->ip_summed == CHECKSUM_PARTIAL) { diff = get_csum_diff(ip6h, p); inet_proto_csum_replace_by_diff(&uh->check, skb, - diff, true); + diff, true, true); if (!uh->check) uh->check = CSUM_MANGLED_0; } @@ -111,7 +111,7 @@ static void ila_csum_adjust_transport(struct sk_buff *skb,
diff = get_csum_diff(ip6h, p); inet_proto_csum_replace_by_diff(&ih->icmp6_cksum, skb, - diff, true); + diff, true, true); } break; }